| Description | The O76(Ec) antigen is currently only known from its antibody reaction, no information about the monomer structure or the genes involved is found in the literature. Genomic information from O76(Ec)-antigen regions sequenced at JCVI (ostec16 and gstec07) provides the basis for this property. From this data we postulate that the antigen is assembled using the wzx/wzy/wzz system, and consistent with this mechanism the three glycosyltransferases present in the locus suggest that there are at least three distinct linkages and at least four sugars in the repeating monomer unit. The sugar composition of the antigen can be guessed at since the locus appear to lack any extra sugar biosynthesis genes beyond those converting UDP-glucose to UDP-galactose and a single putative acetyltransferase. Additionally, two of the glycosyltransferases show homology to transferases associated with the O128(Ec) (GT-1), and the O86(Ec) and O127(Ec) antigens (GT-3). Each of these is composed entirely of L-fucose and D-galactose residues (or their N-acetylated forms). L-fucose is not bioavailable in E. coli without the presence of specialized genes for its biosynthesis, and these are nearly always present in the O-antigen locus when needed. Taken together, we postulate that the O76(Ec) antigen monomer is composed primarily if not exclusively of D-Gal and D-GalNAc residues. |
